This is the transcript of the episode 5 promo available for viewing on Real Player at the official site.

VoiceOver:

VO: The Survivor tribes have been separated by gender...
Rob: There are noooo women around.
VO: ...But when one man and one woman are asked to spend the night together...
Dave: There's a naked girl in the shower that you can see into.
VO: ...You won't believe what happens the morning after.
Heidi: It is a shock to me.
VO: Don't miss a surprising all new Survivor The Amazon Thursday.

You know that if they offered Jenna a chance to be with the guys, she'd turn on her little HCA in a second. And I think if she got to choose who'd go with her, she wouldn't choose anyone who would be competition.

"Look, you love me, and I love you. Maybe in a different time, a different place, this would work out. But we both know that only one of us is leaving this room alive, and I'm the one holding the flame thrower." - Film Fakers

I think a switch seems most likely.
I would hate to think it would be left up to Jenna and Dave to choose the teams though.
I can't really decide what the need was for them to rendezvous.
I'm sure CBS loved the idea that it was two of the younger people, but how were they chosen?
Couldn't it just as easily have been Jeanne and Butch?